PM My Carbine

AR/M4 AR Technical Discussion
1

I’ve jumped into a lot of great threads here and wanted to try to take a stab at putting together a post with all of the ideas I’ve seen on preventive maintenance and hope you guys with armor’s type knowledge jump in. Grant has said this repeatedly here, most folks with military experience don’t know how to maintain an AR past normal field maintenance. That’s me to a T, I was an 03 in the Corps. I know how to use and maintain it in the field. Armor’s level maintenance is a mystery to me and now that I’m footing the bill for my own AR carbine I figure it’s time to learn.

So here’s what I’ve learned about bolt life span and PMs, please chime in if you have more to add. Again, this is not normal care & cleaning but replacing worn parts before your weapon goes to hell. Below is a summary of the items I’ve discussed where replacing/enhancing parts was the topic:

There is an inverse relationship between barrel length to the gas ports and pressure placed upon the BCG. The shorter the barrel (rather the closer the gas port is to the chamber) the greater the pressure on the BCG. Hence a shorter life cycle, same for barrels due to heat induced erosion near the gas ports.

There are devices to mitigate pressure on the BCG but nothing will reduce the erosion near the gas port.

Here are some suggestions from the group on increasing bolt life:
A) Make a super-duper strong bolt/BCG
B) Modify the gas system to vent off some of the pressure
C) Increase the distance of the gas port relative to the chamber

There are other “fixes” that address the symptoms of increased cycle speed due to high pressure:
A) Add a super-duper spring to your extractor
B) Increase the weight of the buffer
C) Increase the tension of the buffer spring

Not a darn thing can be done about barrel erosion around the gas ports.

So, what is the range (in round count) where I should be looking at replacing my barrel?

What round count should I be replacing the bolt?

Springs & things?
I’ve seen a some posts here that say buffer & extractor spring should be replaced after 3 or 5K rounds. What’s the verdict?

Should the trigger group springs be replaced?

Thanks in advance.

2

Im in the same boat as Lowdrag and think something detailing at what round intervals components should be replaced is something worthy of a sticky.

3

Bolts I wouldn’t change until the rifle isn’t headspacing anymore (closing on a NO-GO and FIELD gauge). More than likely a new bolt won’t fix it, this usually requires a new barrel and bolt. I shoot bolts to bolt failure, or when replacing the barrel. New barrel always gets a new bolt (just the way I do it) All springs have a ‘service life’ and all springs will shorten with use. Buffer springs should be checked for length every couple of thousand rounds and when they approach the small end of the spec. they then should be replaced.

I replace the extractor, cam pin, gas rings, extractor pin, extractor spring, ext. buffer and Crane O-ring & FPRP every 3K rounds. I check the firing pin protrusion, buffer spring length, headspace every 3K (I also started keeping a log of the throat erosion in my own ARs). I’m anal and that’s just me. 10K round for a hammer spring isn’t a bad idea, they’re cheap. If replacing the hammer spring at 10K you might as well also replace the disconnector and trigger spring. Mag catch and bolt catch springs I don’t see worn out much but 10-15K rounds wouldn’t be a bad idea to swap out too.

4

When the bbl no longer shoots accurately enough for you. It all depends on the type of metal, lining, rifling method, ammo quality, cleaning practices, etc.
For some HP folks this could be every season.

Pete